Hydroxide cationic functional group, structure

The cationic functional group has been the central focus in HEM chemical structure because it dominates hydroxide conductivity through its basicity as well as its density (i.e., ion exchange capacity, lEC). The intrinsic nature of the functional group also determines solubihty and controls chemical stability. Currently, two major types of cationic functional groups are available one type based on nitrogen atoms and the other type based on phosphorus ones. 

Tris (2,4,6-trimethoxyphenyl) benzyl phosphonium hydroxide shows the highest basicity ever reported. Its HEM has the highest specific hydroxide conductivity among all reported cationic functional group-based HEMs, typically about twice that of trimethyl benzyl ammonium and more than foiu- times that of methyl imidazolium (39 [5], 19 [31], and 8.4mSgcm mmor [32] respectively, with the same polysulfone polymer matrix and homogeneous membrane structure in each case) (Table 6.2). 

---